This invention relates generally to an apparatus for delivering dry collisional damping gas to a mass spectrometer and method, and more particularly to an apparatus which is continuously purged.
Inert gas such as helium is employed for collisional damping of ions within the operating region of mass spectrometers such as in the ion trapping region of an ion trap mass spectrometer. In order to prevent unwanted water-induced ion molecule reactions from occurring within an ion trap, the damping gas must be as free as possible from residual water vapor. Traditional damping gas inlet systems for collisional damping of ions within the ion trap utilize pressure regulators and fixed restrictors in order to control the flow of gas into the mass spectrometer. Since the overall throughput of a damping gas, such as helium, into the trap is in the order of 0.3 cc/min, the time required to eliminate absorbed water vapor due to the large surface area and void volume of regulator diaphragms, plumbing, etc. can be several weeks when first installing and/or starting a mass spectrometer. Furthermore, the hardware employed adds to the cost of the delivery apparatus.
It is a general object of the present invention to provide an improved apparatus and method for delivering dry collisional damping gas into the analyzing region of a mass spectrometer.
It is another object of the present invention to provide an apparatus which is continuously purged.
It is a further object of the present invention to provide an apparatus for delivering damping gas to a mass spectrometer which is simple and inexpensive.
There is provided a collisional gas delivery apparatus which includes a first capillary restrictor of a first internal diameter adapted to have one end connected to a source of pressurized damping gas, a second capillary having a second larger internal diameter having one end connected to the other end of the first capillary, and its other end open to atmospheric pressure. A third capillary restrictor having a diameter less than that of the second capillary restrictor is connected to the common end of the first and second capillary restrictor with its other end adapted for connection to the analyzing region of the mass spectrometer.